This study describes the sound produced by a hydrokinetic turbine operating in a riverine environment near Iguigig, AK (USA). Drifting spar buoys equipped with hydrophones and GPS loggers were used to characterize temporal and spatial variability in turbine sound over a range of turbine operating conditions. Because of the quasi-stationary nature of river flows, multiple replicates could be obtained under steady-state operation. The sound from this turbine consists primarily of tones (ascribed to the generator) and broadband emissions (ascribed to blade vibration). The frequency of the tones varies in proportion to the turbine rotation rate. At the closest point of approach, for an optimally operating turbine, one-third octave levels are elevated by up to 40 dB relative to braked conditions. Broadband spatial patterns suggest relatively limited sound directivity. This study highlights the benefits of using Lagrangian drifters to characterize turbine sound (e.g., flow noise mitigation, spatially-resolved acoustic fields) and challenges (e.g., positional accuracy, self-noise contamination). Further analysis is required to interpret spatial variability in the context of acoustic propagation in riverine environments.